Evaporative refrigeration system

ABSTRACT

Air is evaporatively cooled by water in which the evaporating water is kept separate from the useful air (cooled air stream) by means of a heat exchanger so that cooling is performed without the addition of water vapor to the useful air, and in which the working air, absorbing the water vapor, is drawn from the load. A heat exchanger is disclosed which operates by movement of the working air internally through tubular conduits countercurrently to water flowing downwardly on the inner surfaces thereof while the air to be cooled passes externally across the conduits.

FIELD OF THE INVENTION

The field of art to which the invention pertains includes the field ofair conditioning, more specifically the field of evaporativerefrigeration.

BACKGROUND AND SUMMARY OF THE INVENTION

Evaporative air conditioners have found use in localities where there isa sufficient difference between the dry bulb temperature and thecorresponding wet bulb temperature to provide a desirable heat transfergradient without need for altering the moisture content of the usefulair or for resorting to vapor compression refrigeration. For example, ifthe dry bulb temperature is 93° F and the corresponding wet bulbtemperature is 70° F, there is a difference of 23° F available for airconditioning operation. Early coolers operated by evaporating waterdirectly into the useful air, thereby increasing its moisture level, butsubsequent coolers have been based on the fact that the occupants of anenclosure will experience a greater degree of comfort by cooling the airof the enclosure while maintaining, or reducing, its moisture content.

A variety of sophisticated designs have been proposed and utilizedwherein the heat absorptive action of evaporation is employed to reducethe temperature of heat exchange apparatus and in which air is thenpassed through the apparatus for the purpose of cooling. The air that isused for effecting the evaporation (working air) is conducted to theoutside of the room to be cooled and the air that is cooled by passingthrough the apparatus (useful air) is directed into the room. In thisway, the heat abstracted from the liquid during the evaporation is notredelivered to the air of the room, nor is the moisture content of theuseful air increased. In this regard, one can refer to the followingU.S. Pat. Nos. Re 17,998, 2,044,352, 2,150,514, 2,157,531, 2,174,060,2,196,644, 2,209,999, 2,784,571 and 3,214,936. Additional patents ofinterest are: U.S. Pat. Nos. 1,542,081, 2,488,116 and 3,025,685. In morerecent years, evaporative coolers have been replaced by vaporcompression refrigeration units in which refrigerant fluid isalternately compressed and evaporated in a refrigeration cycle. Suchunits can be made quite compact, but are generally inefficient and,importantly, energy-intensive. Dwindling energy resources have requiredpriorities in this regard to be reexamined and the need for improved,more efficient cooling devices has become evident.

The present invention satisfies the foregoing need in that it provides ahighly efficient apparatus for cooling of air. The device operates moreefficiently by a conjunction of features. Specifically, a heat exchangeris used that separates its dry and wet sides; evaporating water is keptseparate from the useful air so that cooling is performed without theaddition of water vapor to the useful air. Additionally, the majorportion, preferably all, of the working air, is drawn from the load,i.e., the working air is recirculated from the enclosure to be cooled tothe wet side of the heat exchanger. Furthermore, in a preferable mode ofconstruction, the wet side of the heat exchanger operates by movement ofthe working air internally through conduits countercurrently to waterflowing downwardly therethrough along the conduit inner surfaces, whilethe useful air passes through the dry side externally across theconduits.

Specific constructional details for maximum efficiency are givenhereinafter. In a specific embodiment, additional increases inefficiency can be obtained by flowing the moisture-laden return airexhausting from the wet side of the heat exchanger in heat-exchange, butseparated, relationship with fresh air flow upstream from the dry sideof the heat exchanger. In a further embodiment, a composite, hybridsystem is provided in which a minor portion only of the useful air,downstream of the dry side of the heat exchanger, is passed over theevaporator of a vapor compression refrigeration system. A sufficientlysmall amount of the useful air can thus be cooled sufficiently below itsdew point to dehumidify that portion of the air resulting in a greaterreduction in the dry bulb temperature of the useful air. Other featuresare provided which, while decreasing somewhat from the total efficiencyof the basic system, provide a greater degree or rate of cooling thanheretofore possible with evaporative coolers for specializedapplications and/or for high cooling rate usage. In this regard, aparticular embodiment calls for a portion of the returned air to bediverted to mix with the fresh air for further cooling by the heatexchanger. In another particular embodiment, useful under certainclimatic conditions to provide a lower temperature but at higher energylevels, a portion of the cooled useful air emerging from the heatexchanger is diverted to mix with the working return air forcountercurrent contact with the evaporating water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic "circuit" diagram of an evaporative cooler systemembodying basic concepts of the present invention;

FIG. 2 is a diagrammatic elevational view of a specific embodiment ofthe system of FIG. 1;

FIG. 3 is a plan view of a portion of the heat exchanger tube array andheader, taken on line 3--3 of FIG. 2;

FIG. 4 is an enlarged view of a portion of FIG. 3 below the header; and

FIG. 5 is a diagrammatic elevational view of a hybrid evaporative coolersystem which incorporates the components of a vapor compressionrefrigeration unit.

DETAILED DESCRIPTION

As required, detailed illustrative embodiments of the invention aredisclosed herein. The embodiments exemplify the invention and arecurrently considered to be the best embodiments for such purposes.However, it is to be recognized that the units may be constructed invarious other forms different from that disclosed. Accordingly, thespecific structural details disclosed are representative and provide abasis for the claims which define the scope of the present invention.

As above-indicated, the present evaporative refrigeration system is onein which the evaporating water is kept separate from the cooling airstream by means of a heat exchanger so that cooling is performed withoutthe addition of water vapor, achieving sensible cooling. To effect themaximum cooling available at the lowest energy cost, at least a majorportion, preferably all, of the working air used for the wet side of theapparatus is drawn from the room to be cooled (load), because it has alower wet bulb temperature than outside, fresh air and thus a largertemperature differential can be obtained than if fresh air were used forthat purpose. It is also preferred that the major portion of useful air,i.e., air passing through the dry side of the heat exchanger, be freshair. A particularly useful form of apparatus to accomplish the foregoingis one utilizing an array of spaced vertically directed hollow elongatedtubular members. The wet side is accomplished by gravity flow of waterdownwardly along the inner surfaces of the tubes in conjunction withcountercurrent flow of returned air from the load, to exhaust. The dryside is accomplished by fresh air flowing in thermal conductive contactwith the outer surfaces of the tubular members for cooling thereof, thecooled fresh air being delivered to the enclosure.

Referring to FIG. 1, there are illustrated various air flow paths whichcan be utilized by the present embodiment. The system includes a heatexchanger 10 through which fresh air 12 passes on the dry side emergingas two streams 14 and 16 of cooled useful air for flowing to twodifferent zone locations 18 and 20, respectively, of an enclosure 22 tobe cooled. A stream of return air 24 is flowed back to the heatexchanger 10 and constitutes a working fluid for evaporation of waterwithin the heat exchanger 10, as will be described in more detailhereinafter. The moisture-laden return air exits as an exhaust stream26, which, in a particular embodiment, is flowed in heat exchangerelationship, as indicated at 28, with the fresh air 12 before beingdisposed exteriorly of the device and of the enclosure.

In accordance with a particular variation of operation, a portion of thereturn air can be diverted as a recirculation stream 30 to mix with thefresh air 12. By such means, the enclosure can be cooled more quicklythan otherwise, although at a higher energy cost. In accordance withother variations of operation, portions of the cooled air streams 14 and16 can be diverted as by-pass streams 32 and 34, respectively, to mixwith the working return air stream 24, passing through the wet side ofthe heat exchanger 10. Such a configuration is useful under certainclimatic conditions to enable a lower temperature, but again at a higherenergy cost.

Referring now to FIG. 2, the heat exchanger 10 comprises an array ofspaced vertically directed hollow elongated tubular members 36 stackedbetween top and bottom headers 38 and 40, respectively, so as to form adry side enclosure 42 bounded on top and bottom by the headers 38 and40, on the downstream side by a side wall 44 and on the upstream side bya filter 46. The side wall 44 is spaced sufficiently from the array oftubular members 36 so as to accomodate therein a pair of blowers 48 and50. The blowers 48 and 50 are shown stacked one above the other, but maybe disposed laterally adjacent each other. The draw fresh air 12 viaductwork 52 through the filter 46, past the external surfaces of thetubular members 36 in the dry side 42 of the heatexchanger, where thefresh air is cooled, and then distributes the cooled air to ductwork 54and 56, opening into the enclosure 22, as the separate cooled airstreams 14 and 16 referred to above. It is preferred to draw, ratherthan push, the useful air through the heat exchanger as such providesthe most uniform air distribution without recourse to baffles, staticplates or other such devices which would introduce additional resistanceto airflow in the system. By using a pair of blowers 48 and 50, thecooled air can be passed to spaced zones 18 and 20 in the enclosure 22.The blowers 48 and 50 are variable speed blowers which are independentlycontrolled by their own thermostats 58 and 60 located as desiredrespective the enclosure zones 18 and 20 to be cooled.

Ductwork 62 communicates with the enclosure 22 at 64 and conveys returnair 24 to a blower compartment 66 in which in return air blower 68pushes the return air into a plenum 70. The plenum 70 is disposed belowand in communication with the interior surfaces of the tubularmembers 36and is separated from the dry side of the heat exchanger by means of thebottom header 40. The plenum 70 also serves as a sump for containing areservoir of water 72 for evaporation. The water 72 is fed by means of awater pump 74 and a suitable pipeline 76 to an array of manifold tubes78 overlying the top header 38. The water 72 emerges from jets 80 in themanifold tube array 78 onto the top header 38 flowing into anddownwardly along the inner surfaces of the tubular members 36, by theforce of gravity, returning to the plenum 70 and reservoir of water 72therein. The blower 68 pushes the working return air 24 upwardly throughthe tubular member 36 countercurrently to flow of the water 72,resulting in evaporation of a portion of the water 72, therebyabstracting heat from the walls of the tubular members 36. Themoisture-laden air is discharged as an exhaust stream 26 from the top ofthe heat exchanger where it is conducted by ductwork 82 to a point ofdischarge 84. The ductwork 82 is formed with an annular sectionsurrounding the fresh air ductwork 52 to provide a heat exchangeassembly 28 to pre-cool the fresh air 12.

Although the return air 24 is shown as being pushed through the wet sideof the heat exchanger by the blower 68, an alternative, somewhat moreefficient, arrangement is to mount the blower at the top of the heatexchanger to draw the moist air through the wet side and into theductwork 82.

Referring more specifically to the plenum 70, water which is notconsumed in the evaporation process flows from the inner surfaces of thetubular members 36 and drips into the reservoir of water 72. The pump 74can be a submersible pump as shown located within the reservoir of water72, or can be external to the reservoir. Water is introduced into theplenum-sump region by means of a ball-float valve 86 connected to aninput pipe 88. Scale and/or lime formations are minimized by use of ableed-down system defined by a syphon 90. The syphon is located in theplenum, spaced just above the operational level of the reservoir 72 asdetermined by the ball-float valve 86 but below the level reached whenoperation of the unit is terminated. At that time, the reservoir waterlevel will rise due to natural drain-back and the syphon 90 will cause apartial draining or bleed-down to expel contaminated water. Othermethods of reducing contamination build-up, e.g., by means of a bleedline in the discharge line from the pump, can be used.

Other methods of water distribution than the manifold 78 can be used.For example, a trough network can be disposed over the top header 38whereby water flows by gravity through notches in the sides of thetroughs. Alternatively, a water trough system can be constructedintegral with the top header 38 whereby the troughs would be disposedbetween the tubes and the water would flow from the troughs into anddown through the tubes directly.

As earlier indicated, provision is made for recirculation of return airand for bypass of cooled air. With respect to the first provision,ductwork 92 leads from the return ductwork 62 to a region 94 adjacentthe bottom of the fresh air filter 46. By such means, a portion of thereturn air 24 can be diverted, as shown at 98, to mix with the fresh air12, thereby increasing the cooling rate. The amount of return air thusrecirculated can be effected by means of a damper 100 disposed in therecirculation ductwork 92.

With respect to the second provision, ductwork 102 and 104 can beconnected to the supply ductwork 54 and 56 to permit flow of bypasscooled air 32 and 34 therethrough to the return air blower compartment66, regulated by dampers 106 and 108 (the lower portion of the ductwork104 being hidden by the ductwork 102 in the view of FIG. 2). By suchmeans a lower useful air temperature is achieved.

Details of construction of the array of tubular members 36 can be seenin FIGS. 3 and 4. The tubular members 36 are substantially square inexternal cross-sectional configuration, but are formed withsubstantially rounded corners. By using squared tubes, an array matrixcan be obtained that permits greater external surface area than otherconfigurations. The flow cross section extending between the tubes issubstantially uniform, as shown, and is chosen so as to obtain a desiredflow rate of fresh air on the dry side. Referring in particular to FIG.4, in the specific configuration illustrated, the distance 110 betweendiagonally adjacent tubes is about twice the distance 112 betweenlaterally adjacent tubes. In general, the distances chosen with respectto any particular size tubes should be such as to permit the desiredflow rate in the free area between the tubes. Preferably, the externalside dimension of each tube is greater than three times the externaldistance between laterally adjacent tubes and a ratio of about 5.6 isillustrated in FIG. 4. Referring again particularly to FIG. 3, a portiononly of the header 38 is illustrated and the specific tubular arrayillustrated is comprised of 449 tubes arranged in twelve rows of twentytubes each alternating with eleven rows of nineteen tubes each. Theparticular tubes illustrated have a wall thickness of 0.03-0.04 inch.With the specific array illustrated, and an external side dimension of1.25 inch, lateral distance between tubes of 0.225 inch and diagonaldistance between tubes of 0.45 inch, the air "sees" a dry side free areaof 1.79 ft².

Again referring particularly to FIG. 4, the inner surfaces of the tubesare formed with longitudinal grooves 114 which parallel the flow ofwater and wet side air. The grooves serve to draw and spread the waterby capillary action to wet the inner tube surfaces, providing a uniformfilm to enhance the effects of evaporation.

An example of the operating efficiency of the specific apparatus ofFIGS. 2-4, can be calculated for a particular enclosure. With thedampers 100, 106 and l08 closed, with a heat exchanger efficiency of80%, with fresh air at 93° F dry bulb and 70° F wet bulb, afterequilibrium conditions have been obtained, at 1680 feet per minuteoperation, the air supplied to the enclosure will be 71.6° F dry bulb.If the enclosure heat load is 30,000 BTU/hr. the air leaving theenclosure will be 80.8° F dry bulb and 66.2° F wet bulb, with an averageroom or enclosure condition of 76° F dry bulb at 58% relative humidity.If in place of return air from the load, one would use fresh air as theworking air for the wet side of the heat exchanger (70° F wet bulbtemperature ) the resultant cooled enclosure would have an average drybulb temperature of 74.6° F instead of 71.6° F. Accordingly, there isdemonstrated the importance of using the return air as the working fluidon the wet side of the heat exchanger, as provided for by the presentconstruction. Furthermore, while it is not possible to achieve 100%efficiency, an efficiency of as much as 90% can be achieved by anincrease in the number of heat exchange tubes. Under such conditions,with the present type of construction, a useful air stream can beobtained having a dry bulb temperature of 67.8° F.

The foregoing apparatus has a capacity of 30,000 BTU per hour and iscomparable to a vapor compression refrigeration unit of about37,500-42,800 BTU per hour total capacity (3-3.5 tons). Vaporcompression refrigeration units have inherent limitations in thesensible capacity of their cooling coils (between 70 and 80%) whereas anevaporative cooler of the present construction is totally sensible.Furthermore, a comparative vapor compression refrigeration unit wouldrequire power consumption of from 4 to 8 killowatts whereas the aboveillustrated evaporative cooler has a power consumption of about 1to 1.5kilowatts.

Referring now to FIG. 5, as a further embodiment of the invention, acomposite hybrid system is illustrated in which a portion of the cooledair stream is further cooled by heat exchange with the evaporator of avapor compression refrigeration unit. Otherwise, the system issubstantially the same as that illustrated in FIG. 2 except for theommission of the heat exchange ductwork, the lateral disposition of thedry side blowers (one of which 48' only is shown) and resultantmodification of configuration of the associated ductwork 102' and 104'.In this hybrid embodiment, the vapor compression refrigeration unit isdefined by a compressor 116 connected by appropriate refrigerant linetubing 118 to a condenser coil 120 which in turn is connected byrefrigerant line tubing 122 to an evaporator coil 124 connected viarefrigerant line tubing 126 back to the compressor 116. The evaporatorcoil 124 is disposed in the dry side compartment of the heat exchangerdownstream of the tubular members 36' so as to operate in the lowestpossible air temperature region within the apparatus. Only a minorportion, preferably less than 25%, of the cooled air leaving the heatexchanger is contacted by the evaporator coil 124 so that a sufficientdrop in temperature is accomplished in that portion of the cooled airstream to fall below the dew point. If the entire air stream were topass by the evaporator coil, the drop in temperature would beinsufficient to reach the dew point, but with only a small amount of theair being so processed, the dew point is passed and the air isdehumidified. For example, in processing 14% of the cooled air past theevaporator coil 124, a dry bulb reduction of 3.8° F can be obtainedcompared to operation without dehumidification.

The moisture removed from the air, which in the example, is atapproximately 53° F, is collected at the base of the evaporator coil 124and drained to the plenum region 70', by means of an evaporatecollection tube 128. The evaporate water will be of lower temperaturethan the wet bulb temperature of the wet side air and will thereforefurther enhance the performance of the unit. Since the pressure at thewet side is higher than that of the dry side, a "p-trap" 130 is formedat the end of the evaporate collection tube 128, to prevent blow-back ofthe condensed moisture into the dry side. By removing some of themoisture from the useful air, the wet bulb temperature is furtherreduced, so that after circulating through the enclosure or load, it isrecirculated back to pass through the wet side of the heat exchanger asworking air with a lower wet bulb temperature, thereby cooling the heatexchanger tubes toward that lower temperature by evaporating the wateron the wet side. This increases the effectiveness of the heat exchangerresulting in a further depression of the dry bulb temperature of theincoming useful air on the dry side. In the example presented herein,this additional cooling effect reduces the average enclosure temperaturean additional 1° F.

As a further aid to operation and economy, the condenser coil 120 isdisposed in the discharge path of the wet side of the heat exchanger.Accordingly, the condensing process takes place in an air stream of 65°F as opposed to the outside air temperature of 93° F. The combinationresults in significant reductions in energy required to operate thevapor compression refrigeration unit, resulting in a power requirementof only 50% of normal.

I claim:
 1. An evaporative refrigeration system for supplying cooledfresh air for delivery to an enclosure, and utilizing air returnedtherefrom as a working fluid, comprising:heat exchange walls havingopposite first and second exposed surfaces; liquid discharge meansarranged to apply a vaporizable liquid to flow across said firstsurfaces to wet said first surfaces whereby to provide an extended filmof said vaporizable liquid thereon; return means for flowing return airfrom said enclosure over said first exposed surfaces, countercurrentlyto flow of said vaporizable liquid as at least the majority of airflowing over said first surfaces, to evaporate said liquid from saidfirst surfaces to thereby abstract heat from said walls to cool therebysaid second surfaces and moisten said return air, and discharging saidmoistened return air to a position outside of said enclosure. means forflowing fresh air from outside said enclosure into thermal conductivecontact with said cooled second exposed surfaces, as the majority of airflowing into said contact, to cool said fresh air; means for conductingat least a portion of said cooled air to said enclosure; and means forflowing a portion of return air from said enclosure into thermalconductive contact with said second exposed surfaces, as a minor amountof the total air flowing into said contact, and thence into saidenclosure.
 2. The system of claim 1 wherein said recirculating means isformed to enable flow of a mixture of said fresh air and said return airportion into said contact.
 3. The system of claim 1 including divertingmeans for flowing a portion of said cooled air over said moistened firstexposed surfaces as a minor amount of the total air flowing over saidfirst surfaces.
 4. The system of claim 3 wherein said diverting means isformed to enable flow of a mixture of said cooled air portion and saidreturn air over said first surfaces.
 5. The system of claim 1 includingmeans for flowing said moistened return air into heat-exchange butseparated relationship with said fresh air prior to contact by saidfresh air with said second exposed surfaces.
 6. Evaporativerefrigeration apparatus for supplying cooled fresh air for delivery toan enclosure, and utilizing air returned therefrom as a working fluid,comprising:heat exchange walls having opposite first and second exposedsurfaces defining, respectively, wet and dry sides of said apparatus;liquid discharge means arranged to apply a vaporizable liquid to flowacross said first surfaces to wet said first surfaces whereby to providean extended film of said vaporizable liquid thereon; return means forflowing return air from said enclosure through said wet side over saidfirst exposed surfaces, as at least the majority of air flowing oversaid first surfaces, to evaporate said liquid from said first surfacesto thereby abstract heat from said members to cool thereby said secondsurfaces and moisten said return air, and discharging said moistenedreturn air to a position outside of said enclosure; means for flowingfresh air from outside said enclosure through said dry side into thermalconductive contact with said cooled second exposed surfaces, as themajority of air flowing into said contact, to cool said fresh air; acondenser, an evaporator, and a compressor operatively connected byconduits for condensing and evaporating a refrigerant fluid in arefrigeration cycle, said evaporator being disposed within saidapparatus, in the dry side thereof, downstream from said second surfacesfor heat exchange with a minor portion only of said cooled air todehumidify said portion; and means for conducting at least a portion ofsaid cooled air to said enclosure.
 7. The system of claim 6 wherein saidcondenser is disposed in the discharge path of said moistened returnair.
 8. The system of claim 1 wherein said heat exchange walls areformed as a array of spaced hollow elongated conduits defined by saidfirst and second surfaces as inner and outer surfaces, the flowcross-section extending therebetween being substantially uniform.
 9. Thesystem of claim 8 wherein said conduits are vertically directed and saidliquid discharge means is formed to apply said vaporizable liquid to theupper inner surfaces for flow by gravity therethrough.
 10. The system ofclaim 9 including top and bottom headers on opposite sides of saidconduit array isolating the spaces between said conduits from return airdelivered for flow through said conduits.
 11. The system of claim 10wherein said liquid discharge means comprises means for distributingsaid liquid onto said top header for flow into said conduits to wet saidfirst surfaces whereby to provide an extended film thereon to enchancethe effects of evaporation.
 12. An evaporative refrigeration unit forapplying cooled air for delivery to an enclosure, comprising:an array ofspaced vertically directed hollow elongated tubular members, the flowcross-section extending therebetween being substantially uniform; liquiddischarge means for applying a vaporizable liquid to the inner surfacesof said tubular members for flow by gravity therethrough; means forflowing air through said tubular members countercurrently to flow ofsaid vaporizable liquid, to evaporate said liquid by abstracting heatfrom said tubular members and thereby to moisten said air, anddischarging said moistened air to a position outside of said enclosure;means for flowing air into thermal conductive contact with the outersurfaces of said tubular members for cooling thereof, for delivery tosaid enclosure.
 13. The unit of claim 12 including top and bottomheaders on opposite sides of said tubular members isolating spacesbetween said tubes from air supplied for flow through said tubes. 14.The unit of claim 13 wherein said liquid discharge means comprises meansfor distributing said liquid onto said top header for flow into saidtubes to wet the inner surfaces of said tubes whereby to provide auniform film thereon to enhance the effects of evaporation.
 15. The unitof claim 12 wherein said elongate tubular members are substantiallysquare in external cross-sectional configuration with substantiallyrounded corners, the external side dimension of each tube being at leastthree times the external distance between laterally adjacent tubes. 16.The unit of claim 15 wherein the external distance between diagonallyadjacent tubes of said array is about twice said external distancebetween laterally adjacent tubes of said array.
 17. The unit of claim 15wherein the inner surfaces of each tubular member is formed lengthwisewith a plurality of grooves to facilitate sheeting of said vaporizableliquid.
 18. An evaporative refrigeration system for supplying cooledfresh air for delivery to an enclosure, and utilizing air returnedtherefrom as a working fluid, comprising:an array of spaced verticallydirected hollow elongated tubular members; liquid discharge meansarranged to apply a vaporizable liquid to flow across the inner surfacesof said tubular members to wet said inner surfaces, whereby to providean extended film of said vaporizable liquid thereon for flow by gravityof said liquid through said tubular members; return means for flowingreturn air from said enclosure through said tubular memberscountercurrently to flow of said vaporizable liquid as at least themajority of air flowing over said first surfaces, to evaporate saidliquid by abstracting heat from said tubular members and thereby tomoisten said return air, and discharging said moistened return air to aposition outside of said enclosure; means for flowing fresh air fromoutside said enclosure into thermal conductive contact with the outersurfaces of said tubular members as the majority of air flowing intosaid contact, to cool said fresh air, for delivery to said enclosure.